Cathode



Jan.25,f1949. GEROUS I 2,459,841

CATHODE Filed June 8, 1943 INVENTOR. .I GLENN ROUSE Patented Jan. 25, 1949 UNITED smrlazs PATENT OFFICE CATHODE Glenn F. Rouse, Long Branch, N. J.

Application June 8, 1943, Serial No. 490,036y

n 4 claims. (c1. 25o-27.5) (Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 O. G. 757) `and have theadvantage of copious electron emis- -ide disappears, some believing that itpasses outwardly by electrolytic action, and others believing that it passes inwardly to the nickel can and there forms an oxide with the nickel. f

With such a cathode, particularly when used with high potentials, there is a tendency for the oxide coating to scale or flake off. Another difficulty is the tendency for some of the barium or barium oxide material to move from the cathode to the grid, thus encouraging electron emissi-on from the grid, a difficulty known as grid contamination.

The primary object of the present invention is to generally improve electron emission tubes, and particularly oxide type cathodes` A more particular object is to provide a cathode of the oxide type which will be characterized by long life, and will not be subject to flaking off of the oxide material. An ancillary object is to devise an oxide type cathode which will cause only a minimum of grid contamination.

To accomplish the foregoing, and other objects which will hereinafter appear, my invention resides in the electrode elements and their relation be defined in the claims. The specification is accompanied by a drawing in which 2 Y of sheet metal for a cathode can, partiallyformed to desired shape;

Figure 3 shows a further step in shaping `the sheet metal to pr-ovide cavities;

Figure 4 shows the sheet metal bent, and lilled with oxide material;

Figures 5, 6, and 7 correspond to Figures 2, 3, and 4' respectively, but show a modification in which the cavities are dovetail-shaped` in section; and Y Figure 8 is explanatory of a further modication of the invention.

Referring to the drawing, and more particularly to Figures 1 and 1A, the electrode assembly there shown comprises a cathode generally designated l2, surrounded bya grid I4, and an anode .|6. In order to simplify the drawing, only the edge wires of the grid are shown in Figure 1A. It will be understood that in practice the electrode assembly is enclosed within an evacuated vglass envelope, the various electrodes being -'supported by suitable lead-ins passing through appropriate sealed glass stems. The present invention centers primarily in the structure of the cathode I2.

One characteristic feature of my improved cathode is that it is provided with a large number of small recesses containing material characterized by high electron emissivity. In the speciilc case here shown, the cathode can is generally cylindrical, and the recesses arek narrow slots extending longitudinally of the can. These recesses are indicated at I8 in Figures 1 and 1A, and preferably contain a metal oxide material such as barium oxide, with a certain amount of strontium oxide. In Figure 1A the oxide material has been omitted. This material may be initially applied as a carbonate, which is later reduced tothe oxide.

The slots are preferably so shaped as to effectively retainthe said material therewithin. For this purpose the channels may be made deep and very narrow, or, if desired, the channels may be given an undercut shape when viewed in sec- Figure 1 is a horizontal section through an elecn trode assembly embodying features of my invention, said section being taken approximately in the plane of the line l-I of Figure 1A;

Figure 1A is a vertical section taken approximately in the plane of the line lA---IA of Figure 1;

Figure 2 is an end View, drawn to enlarged scale,

tion.` Figures 2,. 3, and Llrillustrate the production of T-shaped undercut channels while Figures 5, 6, and '7 illustrate the production of dovetail-shaped undercut channels.

It will be understood that the. cathode has outside surfaces between the recesses or slots, onto which surfaces a thin layer of oxide or metal .from the reservoir of oxide material may spread or creep when the cathode is heated. If the area ofl the cathode which is coated in this way is not too great,` relative to the area carrying the body of -oxide material, certain advantages are obtainable without sacrificing electron emission. One advantage is that the cathode resistance is reduced. Another is that evaporation of the coating material is decreased. Still another advantage is that flaking of the coating is minimized.

Describing the formation of the .slotted cathode in greater detail, a thin sheet of nickel or other suitable metal, having a width equal to the desired length of the cylindrical cathode, and having a length adequate to provide for the slot formation, is preliminarily bent to the corrugated shape shown in Figure 2. At this stage of manufacture, the width of the slots (exaggerated in the drawing) is approximately that desired, but the height of the slots is made greater than desired. Suitable bars of steel are then placed in the slots and the excess sheet metal above the bars is pressed downwardly to foldthe same outwardly as shown at 22. leaving the sheet 'metal withundercut slots. The resulting sheet of metal isthen bent to cylindrical shape, a part of `the cylinder being indicated in Figure 4. The barium carbonate or equivalent material is then applied'to the outside of the cathode, the slots being substantially filled but the outside surfaces 2l being left bare. Subsequently, when the cathode is heated, the carbonate is reduced to the oxide, and barium metal from the oxide creeps outwardly from the slots onto the outer surfaces24.

Undercut slots of dovetail section may be formed somewhat easier than the undercut T- shaped slots provided in Figure 4. This maybe explained with 'reference toFigures 5, 6, and 7, in which it will be seen thatfa thin sheet of nickel or other metal is preliminarily formed into corrugated or slotted shape as 'shown in Figure 5, following which the sheet is compressed lfrom one side edge toward the other while confining the kcorrugated metal between flat top and 'bottom plates. This produces the dovetail `shape shown in Figure 6. The metal is then bent to cylindrical configuration, as is'partially shownin Figure 7, following which theslots are filled with the barium carbonate or equivalent material. The functioning of this cathode is substantially the same as,previouslyidescribed- It is not essential that the slots Vbe undercut. Open slots may be usedbut in such case are preferably made very narrow, say 4only 10, or at most 20 thousandths of an inch inwidth, and are made deep relative to theirwidth,` say `thousandths of an inch. Such a slotjformation is represented in Figure 8, but in this figure, as in others, the width of the slot is exaggerated for clarity. The corrugated sheet is bent to cylindrical shape and thereafter loaded with the electronemissive material.

In all cases, the slot must not bek made unduly large or coarse,*for it has been found that with too great across-section of oxide material in the slot, the material is 'not suiliciently degassed throughout its Vdepth during evacuation of the tube, and later the tube will prove tobe gassy. y

Reverting to Figure 1^, it will be understood that the grid ring 3!! is supported by means of suitable lead-inanot shown; and that the anode I6 is also supported by appropriate lead-ins, not shown. If the electrode assembly forms apart of an oscillator tube containing resonant loops, the electrodes may be supported bythe said loops. This is the case when the electrode assembly forms a part of a so-called VT-l58 tube, de-

scribed and claimed in acopending application The steel bars are then removed,

ill

4 of Harold A. Zahl, Serial Number 473,556, led January 25, 1943.

The cylindrical cathode can is closed at the top by means of a top disc 32, and is heated by means of a heating filament 34 4disposed within the can. The cathode may be supported in any suitable manner, but that here shown is deemedpreferable. The cathode can is carried on va tubular lead-in 36 of substantial diameter, said lead-in being secured coaxially of the can at the open end thereof. The heater filament 34 is supported and energized by means of a heating current lead-in wire 38, which preferably runs coaxially through the tubular lead-in 36. It will be understood that while coaxial lead-ins 36 and 38 have been broken off short in Figure 1A, for convenience in arranging the figures of the drawing, these lead-ins in practice lmay be substantial in length, and ordinarily pass through a glass stem projecting outwardly from the main glass envelope of the tube.

'The largediameter tubular lead-in 36 isused as a radio frequency path, and is also used as one side of the power supply circuit for vheating the 'filament 34.

It is believed that the methodof constructing and using my improved cathode, as welles the many advantages thereof, will -be apparent from' the foregoing detailed description. The reservoir of available electron-emitting material is very large, for a given size of cathode. It is equivalent to a smooth cathode coated with an extremely thick oxide coating, but the present arrangement is far superior to such a supposed cathode for two reasons. In the present arrangement, the oxide material is securely held by the cathode can, and cannot blister or flake off. In operation, the cathode has all the advantage of using an exceedingly thin oxide coating. In fact, the working coat on the outside of the can is far thinner than any which would be yobtainable when directly coating a can, and consequently adheres tenaciouslyto the can, thus minimizing grid contamination.

It will be apparent that while I have shown and described my invention in several preferred for-ins, many changes and modifications may be made in the structures disclosed withoutdeparting from the spirit of the invention as sought to bedefined in the following claims.

Iclaim:

1. A cathode for an electron emission tube, said cathode having a relatively extensive metal surface provided with a large number of small recesses, said recesses having a smaller width at their outer ends than at their bases containing a metal oxide material of high electron emissivity at relatively low temperature.

2. A cathode for an electron emission tube, said cathode having a surface provided with recesses, said recesses having a smaller width at their outer than at their inner ends and containing a metal oxideof high electron emissivity at relatively low temperature, the-cathode being cylindrical, and the recesses being slots extending longitudinally of said cylinder, said slots being relatively deep, narrow slots, retaining the oxide material therewithin.

3. A cathode for an electron emission tube, -said cathode having a surface provided with recesses, said recesses having a smaller width at their outer than at their inner ends and containing a metal oxide of high electron emissivity at relatively low temperature, the cathode being cylindrical, and the recesses being slots extending longitudinally of said cylinder, said slots being dovetail-shaped in section, retaining the oxide material therewithin.

4. A cathode for an electron emission tube, said cathode having a surface provided with recesses, said recesses having a smaller width at their outer than at their inneil ends and containing a metal `oxide of high electron emissivity at -rela- I tively low temperature, the cathode being cylindrical, and the recesses being slots extending longitudinally of said cylinder, said slots being T-shaped in section, retainingthe oxide material therewithin.

GLENN'F. ROUSE.

REFERENCES CITED The following references are of record in the leV of this patent:

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